This invention relates to a process for preparing alkyl (meth)acrylates. Specifically, the process provides for the synthesis of alkyl (meth)acrylates, the hydrolysis of process impurities into starting materials, and the separation of reaction products and starting materials in one reactor.
Alkyl (meth)acrylates are important monomers in commercial polymerization processes. Conventionally, alkyl (meth)acrylates, such as butyl acrylate (xe2x80x9cBAxe2x80x9d), are commercially prepared by a direct esterification process. Typically, butanol (xe2x80x9cBuOHxe2x80x9d) and acrylic acid (xe2x80x9cAAxe2x80x9d) are reacted in the presence of an acid catalyst thereby yielding butyl acrylate and water. The direct esterification is generally run at elevated temperature and reduced pressure. During the reaction, impurities are formed such as dibutyl ether (xe2x80x9cDBExe2x80x9d), butyl-xcex2-butoxy propionate (xe2x80x9cBBBPxe2x80x9d), butyl-xcex2-hydroxy propionate (xe2x80x9cBBHPxe2x80x9d), butyl-acryloxypropionate (xe2x80x9cBAOPAxe2x80x9d), and acryloxypropionic acid (xe2x80x9cAOPAxe2x80x9d). These impurities, if not converted back to starting materials, result in lower yield.
Such impurities are usually removed from the reactor and treated to produce starting materials which can be reused. As a result, these processes are less efficient and require additional capital investment costs for separate reactors. Furthermore, conventional BA preparation processes operate at reduced pressure, necessitating a need for larger sized equipment. Consequently, there is a need for a more efficient, lower cost butyl acrylate process which converts process impurities back to starting materials, does so in the same reactor in which BA is produced and which can be operated at atmospheric pressure.
The present invention discloses a process of preparing alkyl (meth)acrylates which converts process impurities back to starting materials and further reacts them in one reactor. The addition of water during the direct esterification reaction also provides an alkyl (meth)acrylate preparation process which does not require reduced pressure and facilitates the recovery of starting materials from process impurities. Furthermore, separation of the reaction product, such as BA, and the starting (meth)acrylic acid, such as AA, can also be effected in the reactor. Consequently, the present invention provides a process which is more efficient and economical than conventional alkyl (meth)acrylate preparation processes known in the art.
One aspect of the present invention provides a process which includes: (A) charging a reactor with a C1-C4 alcohol, a (meth)acrylic acid, a strong acid catalyst, and at least 5% by weight water to form a reaction mixture; (B) reacting the reaction mixture to form a C1-C4 alkyl (meth)acrylate and process impurities, wherein the process impurities formed are hydrolyzed in the reactor; and (C) separating the C1-C4 alkyl (meth)acrylate and water formed during the reaction from the reaction mixture.
Another aspect of the present invention provides a process which includes: (A) charging a reactor with butanol, acrylic acid, a strong acid catalyst, and at least 5% by weight water to form a reaction mixture; (B) reacting the reaction mixture to form butyl acrylate and process impurities, wherein the process impurities are hydrolyzed in the reactor; and (C) separating the butyl acrylate and water formed during the reaction from the reaction mixture.
A further aspect of the present invention provides a process which includes: (A) charging a reactor with butanol, acrylic acid, 3.5 to 15% by weight sulfuric acid, 6 to 18% by weight water and at least one inhibitor to form a reaction mixture, wherein the butanol and acrylic acid are charged to the reactor in an acrylic acid to butanol molar ratio of 1:1 to 1:1.7; (B) reacting the reaction mixture to form butyl acrylate and process impurities, wherein the process impurities are hydrolyzed in the reactor; and (C) separating the butyl acrylate and water formed during the reaction from the reaction mixture by azeotropic distillation.
Another further aspect of the present invention provides a reaction mixture, including: acrylic acid, butanol, from 3.5 to 15% by weight sulfuric acid, from 6 to 18% by weight water and from 0.001 to 1.0% by weight 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy.
As used herein, the term xe2x80x9c(meth)acrylicxe2x80x9d acid is meant to include both acrylic acid and methacrylic acid. In a like manner, the term xe2x80x9c(meth)acrylatexe2x80x9d is meant to include both acrylate and methacrylate.
As used herein, BuOH refers to n-butanol, i.e., 1-butanol and the term xe2x80x9cbutanolxe2x80x9d includes within its scope all butanol isomers as well as mixtures thereof.
The term xe2x80x9calkylxe2x80x9d is meant to include branched chain, straight chain or cyclic alkyl groups. As used herein the terminology xe2x80x9c(C1-C4)xe2x80x9d or xe2x80x9c(C1-C10)xe2x80x9d means a group having from 1 to 4 or 1 to 10 carbon atoms per group.
As used herein, the terms xe2x80x9cAA richxe2x80x9d or xe2x80x9cBA richxe2x80x9d are understood to mean fractions or components where AA or BA is the major (greater than 50% by weight) organic component of the composition.
Throughout this specification and claims, unless otherwise indicated, references to percentages are by weight, all temperatures by degree centigrade and all pressures are atmospheric.
FIG. 1 illustrates the equipment and the flow lines utilized in one embodiment of the process of the present invention, including the direct esterification/hydrolysis reactor 1 which is a stirred reactor having a distillation column on top of it; line 2, which carries a vaporized distillate mixture, which includes BA, from 1 to a phase separator 3, the phase separator 3 separates the vaporized distillate into a BA rich organic phase and an aqueous distillate phase; line 11, which carries the BA rich organic distillate separated in 3 forward to a separation section; line 8 which carries the aqueous distillate separated in 3 to line 9 to be recycled to 1, and to line 10 to carry it forward to be treated, generally to recover material from aqueous waste; line 4, which carries the AA rich bottoms from 1 to bleed stripper 5, which is the cracking reactor; line 6, which carries the distillate, including recovered BuOH and AA from 5 to be recycled to 1 through line 22, and to line 7 which carries the distillate from 5 forward to be treated, generally as waste; line 12, which carries the bottoms from 5 forward to be treated, generally as waste and optionally to line 17, which recycles bottoms from 5 to 1; line 13, which may feed inhibitor to the reactor; line 14, which feeds catalyst to the reactor; line 15, which feeds fresh AA and BuOH to the reactor; an optional plug flow reactor 16; an optional line 18 for feeding AA, BuOH, and catalyst to 16; an optional line 19 for taking the material from 16 to 1; line 20, which carries the BuOH, BA, and AA recovered in the separation section from lines 10 and 11 back to the reactor 1; and optional line 21 which returns recovered material to an alternative feed location in reactor 1.
As recited above, in step (A) of the present invention C1-C4 alcohol, a (meth)acrylic acid, a strong acid catalyst, and water are charged to a reactor to form a reaction mixture.
Generally, the C1-C4 alcohol is a branched or straight chain alkanol having 1 to 4 carbon atoms or mixture thereof. Specific examples include, but are not limited to, methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, tert-butanol or mixtures thereof. Furthermore, it is contemplated that the C1-C4 alcohol may be substituted, for example, with halogen, hydroxide, alkoxide, cyano, nitro, etc. In one embodiment, the alcohol is butanol. In a preferred embodiment, the alcohol is n-butanol.
Also present in the reaction mixture is (meth)acrylic acid or substituted meth(acrylic) acid substituted with, for example, with halogen, hydroxide, alkoxide, cyano, nitro, etc. In one embodiment, acrylic acid or methacrylic acid or a mixture thereof is present. In a preferred embodiment, the unsaturated acid is acrylic acid. The (meth)acrylic acid and alcohol are present in a molar ratio of 1:1 to 1:1.7, preferably 1:1.1 to 1:1.6, more preferably 1:1.25 to 1:1.45. It is also contemplated that other unsaturated acids such as crotonic acid, cinnamic acid, maleic acid, fumaric acid, etc., which can participate in a transesterification reaction with an alcohol may be utilized in the process of the present invention.
A strong acid catalyst is also present in the reaction mixture. Suitable examples of such an acid catalyst include, but are not limited to, sulfuric acid, methane sulfonic acid, benzene sulfonic acid, p-toluene sulfonic acid, mixtures thereof, or a polymer supported alkyl sulfonic acids such as AMBERLYST(trademark) 15 resin or NAFION-H(trademark) resin. Generally, the alkyl sulfonic acid is a C1 to C10 alkyl sulfonic acid. In one embodiment, the strong acid catalyst is a sulfur containing acid or sulfur containing polymer supported acid. In a preferred embodiment, the strong acid catalyst is sulfuric acid. The concentration of strong acid catalyst by total weight of the reaction mixture in the direct esterification/hydrolysis reactor is typically 3.5 to 15% by weight, preferably 3 to 12% by weight, and more preferably 5 to 8% by weight.
Water is also present in the reaction mixture provided in step (A). Generally, any water, such as tap water, distilled water or deionized water, suitable for use in a direct transesterification reaction, may be used. Furthermore, at least some of the water provided may be recycled water of reaction which has been removed during separation of the reaction product from the starting materials. The addition of water provides a water reaction medium in the reactor which enables operation under atmospheric conditions and the hydrolysis of reaction byproducts to recover starting materials as well as separation of reaction products from starting materials in one reactor.
At least one inhibitor may also be charged to the reactor in step (A). Typically, from 0.001 to 1.0%, preferably 0.001 to 0.5%, and more preferably 0.001 to 0.1% by total weight of reaction mixture of at least one inhibitor, if used, is present during the direct esterification process to prevent polymerization. Suitable inhibitors include hydroquinone, the mono-methyl ether of hydroquinone, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), 4-hydroxy 2,2,6,6-tetramethyl-1-piperidinyloxy (4HTEMPO), butylated hydroxy anisole, naphthoquinone, anthranil, and combinations thereof. Derivatives of these inhibitors may also be used. Such derivatives include, but are not limited to 4-methacryloyloxy-2,2,6,6-tetramethyl piperidinyl free radical and 4-hydroxy-2,2,6,6-tetramethyl N-hydroxy piperidine. In a preferred embodiment, the at least one inhibitor is 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy. In another embodiment, the at least one inhibitor is 2,2,6,6-tetramethyl-1-piperidinyloxy. In another embodiment, 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy and another inhibitor such as, the methyl ether of hydroquinone are used.
In one embodiment, the alcohol is butanol, the (meth)acrylic acid is acrylic acid, the acid catalyst is sulfuric acid and the inhibitor is 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy. In a further embodiment the water is present at from 6 to 18% by total weight of reaction mixture and strong acid catalyst is present at 3.5 to 15% by total weight of reaction mixture.
As recited above, the present invention utilizes one reactor wherein direct esterification of AA and BuOH; hydrolysis of reaction byproducts including BBBP, BBHP, and BAOPA; and separation of BA and AA are achieved. Generally, any reactor suitable or adaptable for a process wherein a direct esterification reaction, hydrolysis of reaction byproducts formed during the transesterification reaction, and separation of reaction products from starting materials occurs in the reactor may be used. In one embodiment, the reactor may be a stirred tank equipped with a distillation column. In a preferred embodiment, the distillation column may be situated directly on top of the reactor (as in FIG. 1) and may be a fractional distillation column. Generally, the distillation column contains from 20 to 100 trays. It is preferred that the column contains from 20 to 70 trays. It is more preferred that the column contains from 40 to 50 trays. The column has means for feeding AA, BuOH, a strong acid catalyst, water, and at least one inhibitor. The reactor also has means for removing the bottoms.
In step (B) the reaction mixture is reacted to form a C1-C4 alkyl (meth)acrylate and reaction byproducts, while reaction byproducts formed during the reaction are hydrolyzed in the same reactor.
The direct esterification reaction may be run by feeding AA and BuOH through lines 15, 20, and 22 to the direct esterification/hydrolysis reactor 1 in an AA to BuOH molar ratio ranging from 1:1 to 1:1.7, preferably 1:1.25 to 1:1.45. The AA and BuOH may also be fed along with sulfuric acid to a plug flow reactor 16, and then to the direct esterification/hydrolysis reactor 1. Inhibitor, if used, is fed into the reactor using line 13. The AA, BuOH, inhibitor, strong acid catalyst, and water form a reaction mixture in the direct esterification/hydrolysis reactor. The AA and BuOH are reacted to a conversion on AA of from 50 to 95%, preferably 60 to 95%, more preferably 70 to 95%.
During the direct esterification reaction, the reactor must have at least 5% by total weight of reaction mixture of water for efficient hydrolysis operation. Preferably, the reactor has from 6 to 18% by weight water during the direct esterification reaction. More preferably, the reactor has from 8 to 12% by weight water during the direct esterification reaction. Water content may be maintained by returning the condensed and separated aqueous distillate from the reactor through line 9 back to the reactor. Water may also be added through any of the feed lines as is necessary. The water in the reactor hydrolyzes reaction byproducts formed during the reaction. Specific examples of hydrolysis reactions which occur include, but are not limited to, reactions where BBBP is hydrolyzed to 2 BuOH and 1 AA, BBHP is hydrolyzed to 1 BuOH and 1 AA, and BAOPA is hydrolyzed to 1 BuOH and 2 AA.
The direct esterification reaction and hydrolysis are run at a temperature of from 100xc2x0 C. to 140xc2x0 C., preferably 105xc2x0 C. to 135xc2x0 C., and more preferably 115xc2x0 C. to 130xc2x0 C. The direct esterification reaction and hydrolysis are run at pressures from 100 mm Hg to 760 mm Hg. Atmospheric pressure is preferred. The residence time in the direct esterification/hydrolysis reactor is typically from 0.5 to 5 hours, preferably from 1 to 4 hours, and more preferably from 2 to 3 hours.
In step (C), the C1-C4 alkyl (meth)acrylate and water formed during the reaction of the alcohol with the (meth)acrylic acid are separated from the reaction mixture by methods known in the art such as distillation, phase separation, etc. In a preferred embodiment, the C1-C4 alkyl (meth)acrylate and water formed during the reaction are separated from the reaction mixture by azeotropic distillation. In a more preferred embodiment, the C1-C4 alkyl (meth)acrylate is azeotropically distilled with water (aqueous reflux) and BuOH under the conditions described above. Accordingly, the water added to the reaction medium as well as water produced from the transesterification reaction of AA and BuOH provide an aqueous medium which enhances separation of AA and BA in the reactor. The distillate may then be taken through line 2 to a phase separator 3. In the phase separator, an organic phase which is BA rich and contains BuOH, and an aqueous phase which contains water and AA separate. The organic phase may be taken through line 11 to a separation section, wherein pure BA is obtained. BuOH may be recovered from the separation section and recycled. Part of the aqueous phase is taken through line 8 to line 9 to be recycled to the reactor to maintain the appropriate amount of water in the reactor. The rest of the aqueous phase is taken through line 8 to line 10 to carry it forward to be recovered and treated, generally as waste.
The bottoms of the direct esterification reactor contain strong acid catalyst, BA, AA, BuOH, AOPA, BBPA, and BHPA. A bleed stripper 5 may be utilized to crack acryloxy proprionic acid (xe2x80x9cAOPAxe2x80x9d), the dimer of AA; beta-n-butoxy propionic acid (xe2x80x9cBBPAxe2x80x9d), and beta-hydroxy propionic acid (xe2x80x9cBHPAxe2x80x9d). Accordingly, the bottoms may be taken through line 4 to bleed stripper 5 (the cracking reactor), where AOPA is cracked to 2 AA; BBPA is cracked to 1 BuOH and 1 AA; and BHPA is cracked to 1 AA. The cracking reactor may be a continuous stirred tank reactor. Where the cracking reactor is incorporated in the process, the liquid in the cracking reactor is maintained at from 5 to 25% by weight strong acid, preferably sulfuric acid. The cracking reactor is operated at a temperature ranging from 90 to 140xc2x0 C., preferably from 110 to 140xc2x0 C. The cracking reactor is operated at a pressure ranging from 20 to 200 mm Hg, although higher pressures, up to 800 mm Hg may be used. The residence time in the cracking reactor is typically from 0.5 to 10 hours, preferably 0.5 to 6 hours, more preferably 0.5 to 3 hours.
Part of the BA, AA, BuOH and water generated in the cracking reactor may be taken overhead and recycled to the direct esterification/hydrolysis reactor through line 6 to line 22. The rest of the BA, AA, BuOH and water generated in the cracking reactor may be taken overhead through line 6 to line 7 to be carried forward to be treated, generally as waste. The bottoms of the cracking reactor may be taken through line 12 to be carried forward to be treated, generally as waste, or may be recycled to the direct esterification/hydrolysis reactor 1 through line 17.
The following examples illustrate the process of the present invention.
Materials: AA, BA, and BuOH were obtained from plant production streams. The inhibitors used are commercially available.
Analyses: Standard methods were used for determination of water, monomer, BuOH, and residual impurities. AOPA, BBBP, BBHP, and BAOPA levels were determined by gas/liquid chromatography using flame ionization detection. Sulfuric acid determinations were obtained using a pH probe and alcoholic tetrabutylammonium hydroxide titrant.